We have square bales of hay up in the barn loft that our cows devour. We don't know how long those bales have been there, but they are dry. We also use some of the remnants of those bales for the nesting boxes.
Meaning.... those square bales are much older than from 2016, we're thinking about 10 years.

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In memory of our first rooster, a Kindle eBook on Amazon, "Humphrey, the Rooster: A true story".

I was reading some controversy that the chickens will eat it and may become impacted. Some said it is the fresh alfalfa that impacts them and others said the dry stuff. I just thought I would like to get some, as it's free, but I don't want to use it if it is bad for my birds. We use straw and other bedding though and haven't had a problem, so I didn't think hay would be any different. If it is dusty though, my husband might not like it either, due to his allergies.

We are basically using what we have. The bales in the hay loft came with the barn when we moved here in Dec. 2015. I don't think our bales are pure alfalfa; they are most likely a mixture of whatever grew in the fields.
In my hens nesting boxes, on the bottom I put course shavings, then put hay/straw/whatever it is on top. In the summer, I often add some fresh mint and other herbs, and sprigs of mint in every corner of the coops.

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In memory of our first rooster, a Kindle eBook on Amazon, "Humphrey, the Rooster: A true story".